CN111351844B - Vortex detecting device based on superconducting quantum interferometer - Google Patents
Vortex detecting device based on superconducting quantum interferometer Download PDFInfo
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- 238000001514 detection method Methods 0.000 claims abstract description 68
- 238000006073 displacement reaction Methods 0.000 claims abstract description 52
- 230000005284 excitation Effects 0.000 claims abstract description 36
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 114
- 239000007788 liquid Substances 0.000 claims description 56
- 229910052757 nitrogen Inorganic materials 0.000 claims description 56
- 230000004907 flux Effects 0.000 claims description 19
- 238000012360 testing method Methods 0.000 claims description 11
- 239000002887 superconductor Substances 0.000 claims description 7
- 238000007689 inspection Methods 0.000 claims 1
- 238000005259 measurement Methods 0.000 abstract description 10
- 229910001094 6061 aluminium alloy Inorganic materials 0.000 abstract description 7
- 230000008901 benefit Effects 0.000 abstract description 3
- 239000000523 sample Substances 0.000 description 23
- 230000007547 defect Effects 0.000 description 20
- 230000035945 sensitivity Effects 0.000 description 12
- 238000000034 method Methods 0.000 description 10
- 239000000463 material Substances 0.000 description 8
- 229910000838 Al alloy Inorganic materials 0.000 description 7
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- 238000010586 diagram Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 238000004088 simulation Methods 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000005672 electromagnetic field Effects 0.000 description 2
- 230000005358 geomagnetic field Effects 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 2
- 229910004247 CaCu Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 1
- 239000005751 Copper oxide Substances 0.000 description 1
- 230000005668 Josephson effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 229910000431 copper oxide Inorganic materials 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000005674 electromagnetic induction Effects 0.000 description 1
- 239000000696 magnetic material Substances 0.000 description 1
- 238000009659 non-destructive testing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000013139 quantization Methods 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
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Abstract
The invention provides an eddy current detection device based on a superconducting quantum interferometer, which can further improve the detection depth of a sample, and comprises a single-junction superconducting quantum interferometer chip and a cylindrical excitation coil; the exciting coil is positioned between the superconducting quantum interferometer chip and the signal window, and the axis of the exciting coil is perpendicular to the nonmagnetic displacement table; the superconducting quantum interferometer chip is adjacent to the end part of the excitation coil, which is far away from the nonmagnetic displacement table, and the detection center of the superconducting quantum interferometer chip is positioned on the axis of the excitation coil, and the axes of the excitation coil and the junction plane of the superconducting quantum interferometer chip are mutually parallel. The device has the advantages of simple structure, convenient operation and high detection precision, improves the amplitude and the signal-to-noise ratio of the eddy current signal while not exceeding the range of the superconducting quantum interferometer, can detect extremely weak eddy current magnetic field signals, and improves the detection depth. The actual measurement proves that the detection depth of the 6061 aluminum alloy crack sample reaches 32mm.
Description
Technical Field
The invention relates to the technical field of nondestructive testing, in particular to an eddy current testing device based on a superconducting quantum interferometer.
Background
The eddy current detection is a non-contact detection method, and a method for detecting by electromagnetic field and intermetallic electromagnetic induction is one of industrial nondestructive detection methods. The principle is that an exciting coil is used to generate an alternating electromagnetic field, which generates vortex current, namely vortex, in a sample. When various defects such as cracks, gaps, holes, corrosion, gaps and the like exist in the sample, the eddy current is influenced by the defects to change, the magnetic field generated by the eddy current is changed due to the change, and the change can be detected by a magnetic field measuring device, so that the defect information is detected.
The sensor for measuring the magnetic field in the eddy current detection is also called an eddy current probe, the traditional eddy current probe is an induction coil, the cost is low, the structure is simple, the defect is low in low-frequency sensitivity, the detection depth is shallow, and deep defects are difficult to detect. Compared with induction coils, the magnetic field measuring equipment with higher low-frequency sensitivity is more good at detecting defects, and the novel magnetic field measuring equipment such as an anisotropic magneto-resistance sensor, a giant magneto-resistance sensor, a fluxgate magnetometer, a superconducting quantum interferometer and the like all have higher low-frequency sensitivity, so that the magnetic field measuring equipment has the prospect of being applied to deep eddy current detection.
Among these, the sensitivity of superconducting quantum interferometers is the highest of the above devices. The basic principle of a magnetic flux sensor for converting magnetic flux into voltage is based on the superconducting josephson effect and the phenomenon of magnetic flux quantization, and various sensors and measuring instruments are derived based on the phenomenon, and can be used for measuring physical quantities such as magnetic field, voltage, magnetic susceptibility and the like. Specifically, two superconductors separated by a thin barrier layer form a josephson tunnel junction, which exhibits a macroscopic quantum interference phenomenon when the closed loop of the superconductor containing the josephson tunnel junction is biased by a current of appropriate magnitude. However, the process is not limited to the above-described process,the super strong magnetic field can destroy the superconducting state in the Josephson tunnel junction, so that the Josephson tunnel junction loses the magnetic field measurement function, and the measuring range is limited, and the typical direct measuring range is only +/-10 -6 T corresponds to about 1/50 of the geomagnetic field.
Because the coupling mode of the josephson single junction is radio frequency coupling, the noise of the coupling mode is related to the ambient temperature of the magnetic flux locking circuit, while the coupling mode of the josephson double junction is direct current coupling, the noise of the coupling mode is unrelated to the ambient temperature of the magnetic flux locking circuit, and the sensitivity of the double junction is usually slightly higher than that of the single junction. In the existing superconducting quantum interferometer eddy current detection equipment, in order to improve the sensitivity of magnetic field measurement, a double-junction superconducting quantum interferometer chip is generally adopted. However, the chip requires that the magnetic fields on the double junctions are basically balanced, otherwise, the quantum interference equation is changed, so that the normal line of the junction plane and the axis of the exciting coil are required to be parallel, and the annular ring and the exciting coil are coaxially arranged, namely, the double junctions are positioned at one end of the exciting coil and symmetrically arranged at two sides of the axis of the exciting coil. When in measurement, the axis of the exciting coil is required to be perpendicular to the plane of the sample to be measured so as to generate an eddy current magnetic field, so that the junction plane is parallel to the plane of the sample to be measured, the superconducting quantum interference is mainly influenced by magnetic flux perpendicular to the junction plane, the magnetic flux cannot exceed a measuring range, and the eddy current signal is weak due to the small measuring range, so that the advantage of high sensitivity of the superconducting quantum interference is difficult to develop.
Disclosure of Invention
The invention aims to provide an eddy current detection device based on a superconducting quantum interferometer, which can further improve the detection depth of a sample.
The technical scheme adopted for solving the technical problems is as follows: an eddy current detection device based on a superconducting quantum interferometer comprises a superconducting shielding cylinder, a liquid nitrogen container, a magnetic shielding chamber, a nonmagnetic displacement table, a detection element and a driving analysis circuit of the detection element;
the liquid nitrogen container and the nonmagnetic displacement platform are both arranged in the magnetic shielding chamber, and the nonmagnetic displacement platform is positioned outside the liquid nitrogen container adjacently;
the superconducting shielding cylinder is arranged in a liquid nitrogen container from outside to inside, the detection element is arranged in the superconducting shielding cylinder, liquid nitrogen is filled in the liquid nitrogen container, and the superconducting shielding cylinder and the detection element are immersed in the liquid nitrogen;
the superconducting shielding cylinder is a cylinder body with an opening at one end, the opening end and the nonmagnetic displacement table are respectively positioned at two sides of the corresponding inner wall of the liquid nitrogen container, and a signal window for allowing eddy current magnetic field signals to pass through is formed by the inner wall of the liquid nitrogen container corresponding to the opening end of the superconducting shielding cylinder;
the detection element is positioned at the opening end of the superconducting shielding cylinder and is adjacent to the signal window;
the detection element comprises a single-junction superconducting quantum interferometer chip and a cylindrical excitation coil; the exciting coil is positioned between the superconducting quantum interferometer chip and the signal window, and the axis of the exciting coil is perpendicular to the nonmagnetic displacement table;
the superconducting quantum interferometer chip is adjacent to the end part of the excitation coil, which is far away from the nonmagnetic displacement table, and the detection center of the superconducting quantum interferometer chip is positioned on the axis of the excitation coil, and the axis of the excitation coil is ensured to be parallel to the junction plane of the superconducting quantum interferometer chip.
Further, the driving analysis circuit of the detection element comprises a magnetic flux locking circuit, a superconducting quantum interferometer controller, a lock-in amplifier, a signal generator and a computer;
the superconducting quantum interferometer chip is electrically connected with the superconducting quantum interferometer controller through the magnetic flux locking circuit, and the excitation coil is electrically connected with the output end of the signal generator; the signal output end of the superconducting quantum interferometer controller is electrically connected with the signal input end of the phase-locked amplifier, the signal generator is electrically connected with the reference signal end of the phase-locked amplifier, and the signal output end of the phase-locked amplifier is electrically connected with the machine.
Further, the superconducting shielding cylinder is a superconductor product.
Further, the nonmagnetic displacement table is horizontally arranged and positioned below the liquid nitrogen container, and the opening of the superconducting shielding cylinder is downward;
the superconducting quantum interferometer chip, the exciting coil and the nonmagnetic displacement table are sequentially arranged from top to bottom.
Furthermore, the non-magnetic displacement table adopts an electric control non-magnetic displacement table, and a displacement controller of the electric control non-magnetic displacement table is electrically connected with the computer.
Further, the superconducting quantum interferometer controller, the lock-in amplifier, the signal generator, the displacement controller and the computer are all arranged outside the magnetic shielding chamber.
Compared with the prior art, the invention has the beneficial effects that: the invention provides an eddy current detection device based on a superconducting quantum interferometer, which can further improve the detection depth of a sample, has the advantages of simple structure, convenient operation and high detection precision, can improve the amplitude and the signal-to-noise ratio of an eddy current signal while not exceeding the range of the superconducting quantum interferometer, can detect an extremely weak eddy current magnetic field signal, and improves the detection depth. The actual measurement proves that the detection depth of the 6061 aluminum alloy crack sample reaches 32mm.
Drawings
FIG. 1 is a schematic diagram of an eddy current testing device based on a superconducting quantum interferometer of the present invention;
FIG. 2 is a schematic diagram of the structure of a superconducting quantum interferometer chip of the present invention;
FIG. 3 is a numerical simulation result of one-dimensional distribution of vertical components of eddy magnetic field for a 2mm depth defect of an aluminum plate;
FIG. 4 is a numerical simulation result of one-dimensional distribution of eddy current magnetic field parallel components of a 2mm depth defect of an aluminum plate;
FIG. 5 is an experimental measurement of two-dimensional distribution of eddy current magnetic field parallel components of a 2mm depth defect of an aluminum plate;
FIG. 6 is a schematic diagram of the effect of a magnetic field generated by a 10mA current of a 20 turn excitation coil of the present invention on a superconducting quantum interferometer;
FIG. 7 is a one-dimensional distribution schematic diagram of parallel components of an eddy current magnetic field for detecting crack defects under a 6061 aluminum alloy plate with the thickness of 32mm by using an eddy current detection device based on a superconducting quantum interferometer;
FIG. 8 is a one-dimensional distribution diagram of parallel components of an eddy current magnetic field of a crack defect under a 6061 aluminum alloy plate of 10mm thickness detected by a deep eddy current detecting device of a fluxgate magnetometer.
Reference numerals: 1-a superconducting quantum interferometer chip; 2-exciting the coil; 3-a superconducting shielding cylinder; 4-a liquid nitrogen container; 5-liquid nitrogen; 6-a nonmagnetic displacement table; 7-a magnetic shielding chamber; an 8-flux lock circuit; 9-superconducting quantum interferometer controller; a 10-lock-in amplifier; 11-a signal generator; 12-displacement controller; 13-computer.
Detailed Description
The invention will be further described with reference to the drawings and examples.
As shown in fig. 1, an eddy current detection device based on a superconducting quantum interferometer comprises a superconducting shielding cylinder 3, a liquid nitrogen container 4, a magnetic shielding chamber 7, a nonmagnetic displacement table 6, a detection element and a driving analysis circuit of the detection element.
The liquid nitrogen container 4 and the nonmagnetic displacement table 6 are both installed in the magnetic shielding chamber 7, and the nonmagnetic displacement table 6 is positioned adjacent to the outside of the liquid nitrogen container 4. The superconducting shielding cylinder 3 is arranged in the liquid nitrogen container 4 from outside to inside, the detection element is arranged in the superconducting shielding cylinder 3, liquid nitrogen 5 is filled in the liquid nitrogen container 4, and the superconducting shielding cylinder 3 and the detection element are immersed in the liquid nitrogen 5.
The superconducting shielding cylinder 3 is a cylinder body with an opening at one end, the opening end and the nonmagnetic displacement table 6 are respectively positioned at two sides of the corresponding inner wall of the liquid nitrogen container 4, and a signal window for allowing eddy current magnetic field signals to pass through is formed by the inner wall of the liquid nitrogen container 4 corresponding to the opening end of the superconducting shielding cylinder 3.
The detecting element is positioned at the opening end of the superconducting shielding cylinder 3 and is adjacent to the signal window; the detection element comprises a single-junction superconducting quantum interferometer chip 1 and a cylindrical excitation coil 2; the exciting coil 2 is positioned between the superconducting quantum interferometer chip 1 and the signal window, and the axis of the exciting coil 2 is perpendicular to the nonmagnetic displacement table 6;
the superconducting quantum interferometer chip 1 is adjacent to one end part of the excitation coil 2, which is far away from the nonmagnetic displacement table 6, and the detection center of the superconducting quantum interferometer chip 1 is positioned on the axis of the excitation coil 2, and the axis of the excitation coil 2 is ensured to be parallel to the junction plane of the superconducting quantum interferometer chip 1.
As for the circuit portion, since the basic operation principle thereof is not changed, an existing circuit structure can be adopted. The drive analysis circuit of the detection element comprises a magnetic flux locking circuit 8, a superconducting quantum interferometer controller 9, a lock-in amplifier 10, a signal generator 11 and a computer 13; the superconducting quantum interferometer chip 1 is electrically connected with the superconducting quantum interferometer controller 9 through the magnetic flux locking circuit 8, and the exciting coil 2 is electrically connected with the output end of the signal generator 11; the signal output end of the superconducting quantum interferometer controller 9 is electrically connected with the signal input end of the phase-locked amplifier 10, the signal generator 11 is electrically connected with the reference signal end of the phase-locked amplifier 10, and the signal output end of the phase-locked amplifier 10 is electrically connected with the computer 13.
As described above, according to the eddy current testing device based on the superconducting quantum interferometer of the present invention, the superconducting quantum interferometer chip 1 is located at one end of the excitation coil 2, the nonmagnetic displacement table 6 is located at the other end of the excitation coil 2, and the testing center of the superconducting quantum interferometer chip 1 is located on the axis of the excitation coil 2, and it is ensured that the axis of the excitation coil 2 and the junction plane of the superconducting quantum interferometer chip 1 are parallel to each other. As shown in fig. 2, the junction plane is the plane on which the superconducting quantum interferometer chip 1 is located, and the detection center of the superconducting quantum interferometer chip 1 is the position pointed by LAO step-edge in the superconducting quantum interferometer chip 1, that is, the geometric center of the josephson tunnel junction.
Therefore, after the excitation coil 2 is energized, the magnetic induction lines formed at the detection center position of the superconducting quantum interferometer chip 1 and the junction plane of the superconducting quantum interferometer chip 1 are parallel to each other, and only the magnetic field component perpendicular to the junction plane is measured according to the physical characteristics of the superconducting quantum interferometer. Thus, the direction of the magnetic induction lines generated by the excitation coil 2 at the detection center of the superconducting quantum interferometer chip 1 is parallel to the junction plane, while the sample is subjected to the excitation coil 2 to generate eddy currents, and the eddy current magnetic field of the eddy current magnetic field has a larger component perpendicular to the junction plane of the superconducting quantum interferometer chip 1 at the detection center position.
Thus, by locating the detection center on the axis of the excitation coil 2 and ensuring that the excitation coil 2 axis and the junction plane are parallel to each other, the excitation coil 2 generates a magnetic field of amplitude B at the detection center of the superconducting quantum interferometer chip 1 0 Then B is measured by the superconducting quantum interferometer chip 1 0 cos90°＝0。
Therefore, at this time, the excitation coil 2 can apply a stronger magnetic field to the sample to be measured, and the superconducting quantum interferometer chip 1 is less affected by the magnetic field, without causing overranging. Due to B 0 cos 90+=0, theoretically no matter how large the magnetic field amplitude of the excitation coil 2 is, it will not exceed the range of the superconducting quantum interferometer. While the eddy current signal is enhanced, the magnetic field component of the eddy current magnetic field perpendicular to the junction plane of the superconducting quantum interferometer chip 1 is measured, so that the defect information is detected.
In the example shown in the figure, an alternating current having a peak value of about 10mA is applied to the excitation coil 2 of 20 turns thereof, and the magnetic field of the excitation coil 2 is actually measured, and the peak-peak value of the magnetic field generated at the detection center position is about 1.5E-5T, and the included angle between the direction of the magnetic induction line and the junction plane at the detection center position is about 89.4 °, and the ratio of the influence on measurement is about 1%. Therefore, the exciting coil 2 can apply a magnetic field which exceeds the measuring range of the superconducting quantum interferometer by tens of times, but does not exceed the measuring range of the superconducting quantum interferometer, so that the detection depth of a sample is improved, and the detection precision is higher.
The superconducting shielding cylinder 3, the liquid nitrogen container 4, the magnetic shielding chamber 7 and the detection element can be installed in any mode, and only the installation and performance requirements are met, such as a connecting structure adopted in the existing superconducting quantum interference device.
Specifically, the liquid nitrogen container 4 is mainly used for providing liquid nitrogen, and the liquid nitrogen provides necessary working temperature for superconductivity. Thus, the liquid nitrogen container 4 may employ an open tank, a top-window tank, or a closed tank. In the example shown in the figures, however, since the up-and-down arrangement is adopted, in order to facilitate the filling of the liquid nitrogen 5, an open tank is adopted and mounted in the magnetic shielding chamber 7 by means of a mounting seat made of a non-magnetic material. The mounting may be plate-like, but preferably, in the example shown, is provided as a column.
The magnetic shield room 7 can effectively prevent the interference of the external magnetic field to the detection. Meanwhile, magnetic signal noise is shielded through the arrangement of the superconducting shielding barrel 3, and eddy magnetic field signals are allowed to enter the superconducting shielding barrel 3 from a signal window and then are detected by the superconducting quantum interferometer chip 1 positioned at the opening end of the superconducting shielding barrel 3, so that the signal to noise ratio is further improved.
In the example shown in the figure, however, since the superconducting shielding cylinder 3 is immersed in liquid nitrogen 5, the superconducting shielding cylinder 3 is a superconductor article for further improving shielding performance. The superconductor article may be Bi 1.8 Pb 0.2 Sr 2 Ca 2 Cu 3 O 10 The product may be Bi 2 Sr 2 CaCu 2 O 8 Articles, all of which are copper oxide superconductors. The former has a superconducting transition temperature of about-163 ℃; the latter has a superconducting transition temperature of about-188 ℃. The temperature of the liquid nitrogen 5 is-196 ℃, and the liquid nitrogen 5 can provide superconducting transition temperature conditions. Specifically, in the example shown in the figure, bi is used 1.8 Pb 0.2 Sr 2 Ca 2 Cu 3 O 10 The product is prepared.
In the example shown in the figure, for simplifying the structure, the non-magnetic displacement table 6 is arranged up and down, that is, horizontally, and is positioned below the liquid nitrogen container 4, and the superconducting shielding cylinder 3 is opened downwards; the superconducting quantum interferometer chip 1, the exciting coil 2 and the nonmagnetic displacement table 6 are sequentially arranged from top to bottom.
Further, the superconducting shielding cylinder 3 is installed in the liquid nitrogen container 4 through a connector, and the connector is provided between the liquid nitrogen container 4 and a side wall of the superconducting shielding cylinder 3. In addition, when the liquid nitrogen container 4 is of a roof structure, a connector may be provided between the liquid nitrogen container 4 and the ceiling wall of the superconducting shielding cylinder 3.
The eddy current magnetic field signal passes through the signal window of the liquid nitrogen container 4, enters the superconducting shielding barrel 3 from the opening end of the superconducting shielding barrel 3, and is further detected by the superconducting quantum interferometer chip 1. It should be ensured that the inner wall of the liquid nitrogen container 4 corresponding to the open end of the superconducting shielding cylinder 3 is made of a magnetically permeable material, namely: the signal window is a magnetically permeable material article. On this basis, the other parts of the liquid nitrogen container 4 except the signal window can be made of other materials or magnetic permeable materials. In the embodiment shown in the figures, the liquid nitrogen container 4 is made of magnetically permeable material, forming a non-magnetic liquid nitrogen container. The eddy current magnetic field signal can enter the superconducting shielding cylinder 3 through the openings of the liquid nitrogen container 4 and the superconducting shielding cylinder 3 made of a magnetically permeable material. In order to simplify the installation, the open end of the superconducting shielding cylinder 3 is processed into a specific form, so that the end face is a curved surface or a plane matched with the inner wall of the liquid nitrogen container 4, and after the superconducting shielding cylinder 3 is placed in a back-off manner, the inner surface of the liquid nitrogen container 4 and the end face of the open end of the superconducting shielding cylinder 3 are contacted to form a support.
Further, the superconducting quantum interferometer chip 1 is mounted through a chip bracket, the chip bracket can be mounted on the superconducting shielding cylinder 3 or the liquid nitrogen container 4, but in the example shown in the figure, the superconducting quantum interferometer chip 1, the exciting coil 2 and the nonmagnetic displacement table 6 are sequentially arranged from top to bottom, and in order to simplify the mounting, the chip bracket is mounted on the liquid nitrogen container 4. Similarly, the exciting coil 2 is mounted by a coil bracket which is mounted on the liquid nitrogen container 4. The chip support and the coil support are both made of nonmagnetic materials.
The nonmagnetic displacement table 6 may take any form, and may be made of nonmagnetic materials such as copper and aluminum, as long as the movement of the sample is satisfied. For the convenience of sample detection, it is preferable to use an electronically controlled nonmagnetic displacement table 6, and its displacement controller 12 is electrically connected with a computer 13. During detection, the sample is placed on the nonmagnetic displacement platform 6, and the computer 13 controls the movement of the nonmagnetic displacement platform 6 by sending a command to the displacement controller 12, so that the detection of each position of the sample is facilitated. In the example shown in the figures, a non-magnetic linear displacement stage of the type FPSTA-7T34-20 is used in particular. During measurement, the superconducting quantum interferometer controller 9 adjusts the working state of the superconducting quantum interferometer chip 1 to a magnetic flux locking mode through the magnetic flux locking circuit 8; the signal generator 11 sends an excitation signal to the excitation coil 2 and sends a reference signal to the lock-in amplifier 10 according to the excitation signal. The validity of the signal can be judged by comparing the output signal of the superconducting quantum interferometer controller 9 with the reference signal, and if the output signal of the superconducting quantum interferometer controller 9 is identical to the reference signal in phase and frequency, the signal is valid. During detection, a sample to be detected generates an eddy current magnetic field under the action of the exciting coil 2 and is detected by the superconducting quantum interferometer chip 1, the detection signal is transmitted to the lock-in amplifier 10 through the magnetic flux locking circuit 8 and the superconducting quantum interferometer controller 9, the lock-in amplifier 10 performs denoising and amplifying treatment according to the detection signal and the reference signal, a detection signal is further formed, and finally, the computer 13 performs treatment and output according to the detection signal to obtain defect information of the sample.
In order to prevent the components from interfering with the detection of the superconducting quantum interferometer chip 1, in the example shown in the figure, the magnetic flux lock circuit 8, the superconducting quantum interferometer controller 9, the lock-in amplifier 10, the signal generator 11, the displacement controller 12 and the computer 13 are all installed outside the magnetic shielding room 7. The magnetic shielding chamber 7 can play a role in shielding electromagnetism, prevents the magnetic flux locking circuit 8, the superconducting quantum interferometer controller 9, the lock-in amplifier 10, the signal generator 11, the displacement controller 12 and the computer 13 from interfering the detection of the superconducting quantum interferometer chip 1, and further improves the detection precision.
The device can adopt the related processing program and the computing process of the existing superconducting quantum interferometer in the processing and computing process of the related information, and calculate the influence of the defect on the parallel component of the eddy magnetic field by a numerical simulation method, and firstly deduce a Helmholtz equation by a Maxwell equation set and ohm law; secondly, solving a Helmholtz equation to obtain a real part and an imaginary part of an electric field; finally, calculating the magnetic field generated by the eddy current according to the Piaon-savart formula:
by changing the position of the defect, a curve of the change of the amplitude of the eddy current magnetic field along with the position of the defect can be obtained, and the larger the change amplitude is, the higher the sensitivity of eddy current detection is.
The effect of the eddy current testing device based on the superconducting quantum interferometer is further described below with reference to experimental results. The 20 turns exciting coil is adopted, the output signal of the signal generator 11 is sinusoidal, the frequency is 69Hz, the amplitude is 0.4Vpp, and the current is 10mA. The reference signal of the lock-in amplifier 10 is supplied from the signal generator 11, also 69Hz, and the lock-in amplifier 10 can output a detection signal of this frequency. The output signal of the superconducting quantum interferometer is shown in fig. 6, is a sine signal, has the amplitude of about 1.2E-7T, and the frequency is proved to be 69Hz by measuring the peak distance of the signal, so that the superconducting quantum interferometer belongs to an effective signal.
A6061 aluminum alloy crack sample is placed on a non-magnetic displacement table 6, a 6061 aluminum alloy plate with the thickness of 32mm is covered on the non-magnetic displacement table 6, the movement of the non-magnetic displacement table 6 is controlled through a computer 13, an eddy current magnetic field of the aluminum alloy plate is measured, a voltage signal is output, the voltage signal is in direct proportion to the amplitude of the eddy current magnetic field, and eddy current magnetic field amplitude data are analyzed.
The acquired eddy current magnetic field signals are shown in fig. 7, wherein peaks and troughs of the eddy current magnetic field are the characteristics of the eddy current magnetic field signals of the linear defect or the linear crack, and the characteristic signals of the aluminum alloy crack sample are indicated. The tooth shapes on the wave crest and the wave trough are noise signals. The peak-to-peak value of the aluminum alloy crack eddy current magnetic field signal amplitude is about 4.3E-11T, about one part per million of the geomagnetic field belongs to a very weak magnetic field, and therefore the influence of magnetic field noise is large, the amplitude of noise fluctuation can be estimated approximately to be about 4E-12T from FIG. 7, the signal to noise ratio is about 10, and the defect signal of the aluminum alloy plate can be clearly distinguished. By changing the position of the defect, a curve of the change of the amplitude of the eddy current magnetic field along with the position of the defect can be obtained, and the larger the change amplitude is, the higher the sensitivity of eddy current detection is.
To verify the correctness of the numerical simulation method, experimental measurements were performed on the parallel components of the eddy magnetic field, the results of which are shown in fig. 4. Comparing fig. 4 and fig. 5, the eddy current magnetic field amplitude is in the same order of magnitude, verifying the correctness of the numerical simulation method.
For comparison and verification, the aluminum alloy crack sample was placed on a fluxgate magnetometer deep eddy current testing device, which was shallower than the present invention, so that only a 6061 aluminum alloy plate 10mm thick was covered above, and the measured eddy current magnetic field signal is shown in fig. 8. Fig. 7 is compared with fig. 8 and the waveforms of the two are consistent, which verifies that the eddy current magnetic field signal of the aluminum alloy crack is actually measured by the invention. In fig. 8, the peak-to-peak value of the eddy current magnetic field signal amplitude is about 4.6E-8T, whereas the signal amplitude measured by the invention in fig. 7 is only one thousandth of that of the fluxgate magnetometer, which shows that the sensitivity of the invention to magnetic field is very high, and the invention is suitable for detecting extremely weak magnetic field, thereby greatly improving the eddy current detection depth.
The junction plane of the traditional superconducting quantum interferometer eddy current detection device is perpendicular to the axis of the exciting coil, so that the magnetic induction lines formed by the exciting coil after being electrified are parallel to the normal line of the junction plane at the position where the junction is located. Thus, with respect to the parallel component of the present invention, it is detected as the vertical component of the eddy current magnetic field, and the vertical component of the eddy current magnetic field varies with the amplitude of 6.54E-8T as shown in FIG. 3.
For ease of understanding, the above-mentioned parallel component may be understood as the component parallel to the measuring platform, the perpendicular component may be understood as the component perpendicular to the measuring platform, and the axis of the excitation coil perpendicular to the measuring platform, the chip detecting the magnetic flux perpendicular to its junction plane. Therefore, in the conventional superconducting quantum interferometer eddy current testing device, the junction plane thereof is perpendicular to the axis of the exciting coil, and the vertical component is measured; the junction plane of the superconducting quantum interferometer of the invention is parallel to the axis of the exciting coil, and the parallel component is measured.
The amplitude is 2.16E-7T for a parallel component profile of an eddy current magnetic field such as that shown in FIG. 4. It follows that under the same conditions, the parallel component of the eddy current magnetic field is approximately 3 times the perpendicular component, and the sensitivity of measuring the parallel component is higher. Therefore, the method for measuring the parallel component of the eddy current magnetic field is adopted, and compared with the traditional eddy current detection method, the sensitivity is higher.
The above is a specific embodiment of the invention, and it can be seen from the implementation process that the invention provides an eddy current detection device based on a superconducting quantum interferometer, which can further improve the detection depth of a sample, has simple structure, convenient operation and high detection precision, improves the eddy current signal amplitude and the signal-to-noise ratio while not exceeding the range of the superconducting quantum interferometer, can detect extremely weak eddy current magnetic field signals, and improves the detection depth. The actual measurement proves that the detection depth of the 6061 aluminum alloy crack sample reaches 32mm.
Claims (6)
1. An eddy current testing device based on superconducting quantum interferometer, which is characterized in that: the device comprises a superconducting shielding cylinder (3), a liquid nitrogen container (4), a magnetic shielding chamber (7), a nonmagnetic displacement table (6), a detection element and a driving analysis circuit of the detection element;
the liquid nitrogen container (4) and the nonmagnetic displacement table (6) are both arranged in the magnetic shielding chamber (7), and the nonmagnetic displacement table (6) is positioned at the adjacent outside of the liquid nitrogen container (4);
the superconducting shielding cylinder (3) is arranged in the liquid nitrogen container (4) from outside to inside, the detection element is arranged in the superconducting shielding cylinder (3), liquid nitrogen (5) is filled in the liquid nitrogen container (4), and the superconducting shielding cylinder (3) and the detection element are immersed in the liquid nitrogen (5);
the superconducting shielding cylinder (3) is a cylinder body with one end open, the open end and the nonmagnetic displacement table (6) are respectively positioned at two sides of the corresponding inner wall of the liquid nitrogen container (4), and a signal window for allowing eddy current magnetic field signals to pass through is formed by the inner wall of the liquid nitrogen container (4) corresponding to the open end of the superconducting shielding cylinder (3);
the detection element is positioned at the opening end of the superconducting shielding cylinder (3) and is adjacent to the signal window;
the detection element comprises a single-junction superconducting quantum interferometer chip (1) and a cylindrical excitation coil (2); the exciting coil (2) is positioned between the superconducting quantum interferometer chip (1) and the signal window, and the axis of the exciting coil (2) is perpendicular to the nonmagnetic displacement table (6);
the superconducting quantum interferometer chip (1) is adjacent to one end part of the excitation coil (2) far away from the nonmagnetic displacement table (6), and the detection center of the superconducting quantum interferometer chip (1) is positioned on the axis of the excitation coil (2) and ensures that the axis of the excitation coil (2) is parallel to the junction plane of the superconducting quantum interferometer chip (1).
2. An eddy current testing apparatus based on a superconducting quantum interferometer as claimed in claim 1 wherein: the drive analysis circuit of the detection element comprises a magnetic flux locking circuit (8), a superconducting quantum interferometer controller (9), a lock-in amplifier (10), a signal generator (11) and a computer (13);
the superconducting quantum interferometer chip (1) is electrically connected with the superconducting quantum interferometer controller (9) through the magnetic flux locking circuit (8), and the exciting coil (2) is electrically connected with the output end of the signal generator (11); the signal output end of the superconducting quantum interferometer controller (9) is electrically connected with the signal input end of the phase-locked amplifier (10), the signal generator (11) is electrically connected with the reference signal end of the phase-locked amplifier (10), and the signal output end of the phase-locked amplifier (10) is electrically connected with the computer (13).
3. An eddy current testing apparatus based on a superconducting quantum interferometer as claimed in claim 1 wherein: the superconducting shielding cylinder (3) is a superconductor product.
4. An eddy current testing apparatus based on a superconducting quantum interferometer as claimed in claim 1 wherein: the nonmagnetic displacement table (6) is horizontally arranged and positioned below the liquid nitrogen container (4), and the superconducting shielding cylinder (3) is downward in opening;
the superconducting quantum interferometer chip (1), the exciting coil (2) and the nonmagnetic displacement table (6) are sequentially arranged from top to bottom.
5. An eddy current testing apparatus based on a superconducting quantum interferometer as claimed in claim 2, wherein: the non-magnetic displacement table (6) adopts an electric control non-magnetic displacement table, and a displacement controller (12) of the electric control non-magnetic displacement table is electrically connected with a computer (13).
6. The eddy current inspection apparatus based on superconducting quantum interferometers of claim 5, wherein: the superconducting quantum interferometer controller (9), the lock-in amplifier (10), the signal generator (11), the displacement controller (12) and the computer (13) are all arranged outside the magnetic shielding chamber (7).
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